Reid Vapor Pressure Calculator

Calculator Input

Stock type

Calculation mode

Output pressure unit

Stock temperature

Temperature unit

True vapor pressure input

True pressure unit

Known Reid vapor pressure

Known RVP unit

ASTM D86 slope at 10% evaporated

Slope unit

Graph minimum temperature

Graph maximum temperature

Graph temperature unit

This page estimates RVP and related true vapor pressure for screening studies. It is not a certified compliance test.

Example Data Table

Case	Mode	Stock Temperature	Slope	Known / Solved RVP	True Vapor Pressure
Refined stock example	Known RVP → true pressure	95.0 °F	4.0 °F/vol%	9.00 psi	8.88 psia
Refined light stock	Known RVP → true pressure	80.0 °F	5.5 °F/vol%	12.00 psi	9.52 psia
Crude oil screening	Known RVP → true pressure	90.0 °F	Not required	10.00 psi	11.87 psia

These examples illustrate the page logic and help verify a fresh installation.

Formula Used

1) Refined petroleum stock screening equation

P = exp{ [0.7553 − 413/(T + 459.6)] × √S × log10(RVP) − [1.854 − 1042/(T + 459.6)] × √S + [2416/(T + 459.6) − 2.013] × log10(RVP) − 8742/(T + 459.6) + 15.64 }

P = stock true vapor pressure in psia, T = stock temperature in °F, S = ASTM D86 slope at 10% evaporated in °F per vol%, RVP = Reid vapor pressure in psi.

2) Crude oil screening equation

P = exp{ [2799/(T + 459.6) − 2.227] × log10(RVP) − 7261/(T + 459.6) + 12.82 }

P = stock true vapor pressure in psia, T = stock temperature in °F, RVP = Reid vapor pressure in psi.

3) Vapor-pressure constants reported by this calculator

For refined stock: A = 15.64 − 1.854√S − (0.8741 − 0.3280√S)ln(RVP) and B = 8742 − 1042√S − (1049 − 179.4√S)ln(RVP)

For crude oil: A = 12.82 − 0.9672ln(RVP) and B = 7261 − 1216ln(RVP)

When you choose solve mode, the page numerically inverts the selected equation with a bisection solver until the calculated true pressure matches your entered value.

How to Use This Calculator

Choose the stock type. Use refined mode for light refined petroleum stocks. Use crude mode when slope data is unavailable and you are screening crude oil.
Select the calculation direction. Solve mode estimates RVP from a known true vapor pressure. Forward mode predicts true vapor pressure from a known RVP.
Enter the stock temperature and its unit. The equations internally convert to °F because that is how the engineering correlations are defined.
For refined stock mode, enter the ASTM D86 slope at 10 percent evaporated. This affects the volatility estimate and should match your distillation data.
Choose graph limits to build a temperature-versus-true-pressure profile. The chart helps visualize how the same stock behaves over a wider operating range.
Click calculate. The page shows RVP, true pressure, converted units, constants A and B, warnings, and export controls for CSV and PDF reports.

FAQs

1) What does this calculator estimate?

It estimates Reid vapor pressure or true vapor pressure for petroleum stocks using engineering correlations. It is useful for screening, studies, trend checks, and quick reporting.

2) Is this result the same as a certified laboratory test?

No. This page is an engineering estimator. Regulatory, product release, or contractual work should rely on the applicable laboratory method and documented sampling practice.

3) When should I use refined stock mode?

Use refined mode for light refined petroleum stocks when you know the ASTM D86 slope at 10 percent evaporated. That slope materially changes the calculated relationship between true pressure and RVP.

4) Why is slope required in refined mode?

The refined-stock equation includes the ASTM D86 distillation slope. Without it, the model cannot represent front-end volatility behavior as intended by the screening correlation.

5) Why can true vapor pressure differ from RVP?

They are related but not identical properties. RVP comes from a specific petroleum test framework, while true vapor pressure describes vapor behavior at the selected stock temperature.

6) What do constants A and B mean here?

They are vapor-pressure equation constants reported for engineering convenience. They help summarize the current volatility relationship and can support comparison across cases or internal documentation.

7) Can I use Celsius or metric pressure units?

Yes. The page accepts multiple temperature and pressure units, converts them internally, and reports output in the pressure unit you choose.

8) What should I do if I see a warning?

Warnings mean the case may sit outside the best screening range or need direct testing. Review your stock type, slope quality, and whether a laboratory method is more appropriate.